Well, there's several different things here,
Now, I'm NO EXPERT on riding motorcycles, there's guys here who've been doing it for many years longer than I have, but I'll tell ya what little I know.
They DO make motorcycles w/an automatic transmission, if you want them. Obviously, this isn't as good on gas as the manual shifted bikes.
The clutch on a motorcycle will usually be your left "handbrake" .. a lever you squeeze to disengage the clutchplates, (IIRc, motorcycles use a multi-disk clutchpack, as opposed to a single-disk dry plate, like cars, )
the shifter for he manual bikes will usually be by your left foot. The bike I ride (a friend's) is a 5 speed, 1 down, 4 up. (Meaning ,from neutral, to get to first, I kick the shifter down, then to go to 2nd and on up, the lever is kicked up. It works just like a ratchet, )
You shouldn't have any problem finding a bike that'll fit you.